Strange situation with Woocommerce and featured image inside product

Hi, I have Connections theme in one site. This is what happens:

I upload a product in Woocommerce and I assign a featured image. It has a black background. I enter to the link and I see it.
But if I refresh the link or I enter again, the product page shows me a different file where Woocommerce apllied an opacity.

Which could be the reason? There is not cache, no plugins related to edit images, etc.

Thanks,
Francisco